Calculating power required to ascend a gradient

Notifitsraining

I am interested gaining an idea of how much power I need to generate to successfully complete the climbs on some of the longer events I intend to ride this year, to compare that with the power I can maintain in training at the moment, and to see how much a bit more weight loss will help etc

Machinehead have software on line but it looks very complicated as they have included so many variables. Are there any simpler 'rule of thumb' methods of calculating power required to shift mass of bike & rider up a certain gradient at a certain speed (in my ideal world I imagine someone like Sheldon Brown having compiled tables or a simple calculator to do this - but I can't find anything)?

GavH

This might be worth a look.

http://www.analyticcycling.com/

chrisw12

I've been thinking about this question for a while but haven't bothered to find/work out an answer.

I get a bit fed up of people saying that hill climbing is hard and that certain hills are harder than others. To me this is all non sense. If I ride a flat tt at 300w for one hour, this is just as hard as riding up a hill for 1hr at 300w. (given correct gearing)

So I think you've hit the nail on the head with your question. Rather than asking 'is that hill too hard for me' or 'what gearing do I need to get up it' you should be asking 'what power do I need to be able to generate to get up it'.

Can you provide any power, weight figures for yourself?

Bhima

chrisw12 wrote:

If I ride a flat tt at 300w for one hour, this is just as hard as riding up a hill for 1hr at 300w. (given correct gearing)

You overheat more on a climb so this is not necessarily true.

jibberjim

chrisw12 wrote:

I get a bit fed up of people saying that hill climbing is hard and that certain hills are harder than others. To me this is all non sense. If I ride a flat tt at 300w for one hour, this is just as hard as riding up a hill for 1hr at 300w. (given correct gearing)

There are other differences between flat riding and hill riding other than simply gearing. The inertial load is very different in the two situations, so how you put out 300 watts in the two situations is different.

GeorgeShaw

Well you can complete the climb on very low power if your gearing is low enough ...

But of course you mean whether you can get up without grinding a ridiculously low cadence on your current gearing.

You can calculate your approximate power output for any given climb using the formula: watts = (weight_in_kgs * 9.81 * height_in_metres * 1.1) / time_in_seconds.

I can't remember where the 9.81 and 1.1 come from but they are factors like rolling resistance, etc.

chris halford

:? :? :? :? power only important to how much you weigh :idea: :idea: :idea:

Limburger

GeorgeShaw wrote:

Well you can complete the climb on very low power if your gearing is low enough ...

But of course you mean whether you can get up without grinding a ridiculously low cadence on your current gearing.

You can calculate your approximate power output for any given climb using the formula: watts = (weight_in_kgs * 9.81 * height_in_metres * 1.1) / time_in_seconds.

I can't remember where the 9.81 and 1.1 come from but they are factors like rolling resistance, etc.

9.81 (ms2) is the acceleration (down the hill) due to gravity. You need the angle of the slope in there too for it to make sense.

Its pretty simple physics but it was a long time ago and I hated physics. all the teachers seemed like bell-ends.

Notifitsraining

In answer to Chrisw12, I am currently 87kgs (around 13st 9lbs), though with a little more upper body atrophy along with loss of fat I should be able to get down to 83-4kgs by the end of May - still not light!

My two concerns are peak power required for very steep sections of UK sportives, and the extended efforts required on longer hills, for example in the Dragon Ride or European events. My ‘plan’ to gauge my readiness for extended efforts was to try to calculate the likely power requirement for my weight for a certain average gradient, then ride steadily for an hour or two before using a spin bike at the local gym to see if I can maintain that power level. I would record my heart rate throughout, then incorporate extended efforts at that heart rate level into some of my longer rides.

Does this sound reasonable or is it a bit of an over simplification? It wouldn’t tell me whether my gearing is lower enough – I guess that requires some spring training in the hills to see how it feels, though the site GavH suggests appears to try to incorporate gearing into the calculations.

twotyred

Weight of bike and rider in kg x acceleration due to gravity (9.8 m/s/s) x height gain in metres gives you the work you have done in Joules. Divide this by the number of seconds the climb took gives you your power output in watts. Add on 10% to account for friction, wind resistance and the horizontal component of your travel. Seems to be pretty accurate for hills between 5%-10% gradient that take at least 7 mins to get up, at least compared to my FTP power in the gym although I don't have an on bike power meter to be sure.

chrisw12

jibberjim wrote:

chrisw12 wrote:

I get a bit fed up of people saying that hill climbing is hard and that certain hills are harder than others. To me this is all non sense. If I ride a flat tt at 300w for one hour, this is just as hard as riding up a hill for 1hr at 300w. (given correct gearing)

There are other differences between flat riding and hill riding other than simply gearing. The inertial load is very different in the two situations, so how you put out 300 watts in the two situations is different.

I didn't want to over complicate things by bringing this in, but since you have, for me personally it is much easier to produce 300w on a climb than it is on the flats, so I'd argue (for me) hill climbing is much easier. So again emphasising my point a hour on a hill is much easier than a hour flat tt'ing. :shock: I wish people would stop this fascination with the 'which is the hardest hill question' a hour flat tt'ing will be harder than any hill in the UK.

chrisw12

Notifitsraining wrote:

In answer to Chrisw12, I am currently 87kgs (around 13st 9lbs), though with a little more upper body atrophy along with loss of fat I should be able to get down to 83-4kgs by the end of May - still not light!

My two concerns are peak power required for very steep sections of UK sportives, and the extended efforts required on longer hills, for example in the Dragon Ride or European events. My ‘plan’ to gauge my readiness for extended efforts was to try to calculate the likely power requirement for my weight for a certain average gradient, then ride steadily for an hour or two before using a spin bike at the local gym to see if I can maintain that power level. I would record my heart rate throughout, then incorporate extended efforts at that heart rate level into some of my longer rides.

Does this sound reasonable or is it a bit of an over simplification? It wouldn’t tell me whether my gearing is lower enough – I guess that requires some spring training in the hills to see how it feels, though the site GavH suggests appears to try to incorporate gearing into the calculations.

Great, I can answer those question pretty directly for you as I commute/train on the Rhigos (part of the Dragon ride) I also have some steep hills eg (Aberdare-Maerdy around 16% at the start). I'm also carrying the same sort of weight this time of year.


So here goes.

For Rhigos At winter weight 300w gets me to the top in about 20mins. At summer weight (less clothes and sweat) about 18 mins (big difference hey.) I think about 220w would get me up there at a doable speed. I think though any less could be close to stalling/crawling. I haven't seen anyone fail the Rhigos because the power requirements are pretty low.

Now for my 16%er, it takes me a min of 300w just to get up there, but this is for a short burst of say 2 min.

Not big numbers, but I've seen people fail this hill at the end of a long ride just because they are unable to produce the power needed after a lot of miles in the legs.

chrisw12

Bhima wrote:

chrisw12 wrote:

If I ride a flat tt at 300w for one hour, this is just as hard as riding up a hill for 1hr at 300w. (given correct gearing)

You overheat more on a climb so this is not necessarily true.

Even though in theory you are correct, can you point to one day in the last 5 years where in this country it has been so hot (in the mountains) that it might cause you to overheat and thus lose power?

lloydy75

Sitting in Lanzarote airport as I type, having spent a week out here cycling 5 days, what I found harder was riding on the flat into the wind rather than the long drags of riding mostly up hill for 40 to 50 mins. (wife just informs me we got a 2 hour delay :evil: )

GeorgeShaw

chrisw12 wrote:

For Rhigos At winter weight 300w gets me to the top in about 20mins. At summer weight (less clothes and sweat) about 18 mins (big difference hey.) I think about 220w would get me up there at a doable speed. I think though any less could be close to stalling/crawling. I haven't seen anyone fail the Rhigos because the power requirements are pretty low.

That makes sense, I'm 70kg and at about 200 watts I get up in about 25 minutes without too much pain.

But I can put out much much more than that for a couple of minutes, which is what gets me up 15% gradients. Sustainable power and short-term power are entirely different, except that multiple short-term efforts will add up unless you have sustainable power to back it up.

Pokerface

chrisw12 wrote:

I didn't want to over complicate things by bringing this in, but since you have, for me personally it is much easier to produce 300w on a climb than it is on the flats, so I'd argue (for me) hill climbing is much easier. So again emphasising my point a hour on a hill is much easier than a hour flat tt'ing. :shock: I wish people would stop this fascination with the 'which is the hardest hill question' a hour flat tt'ing will be harder than any hill in the UK.

But there are no hills in the UK that take an hour to get up! Longest one is all of about 20 minutes!

(But if not in the UK - I agree with you. It's easier to do higher wattages for longer times when on an incline.)

Bhima

chrisw12 wrote:

Even though in theory you are correct, can you point to one day in the last 5 years where in this country it has been so hot (in the mountains) that it might cause you to overheat and thus lose power?

There were a lot of very hot days in the peaks last year, but that is irrelevant. It can be zero degrees and you will still be hotter on a climb, compared to the flat. You might not overheat, but you will certainly be hotter.

Pokerface

chrisw12 wrote:

Even though in theory you are correct, can you point to one day in the last 5 years where in this country it has been so hot (in the mountains) that it might cause you to overheat and thus lose power?

July 19, 2006 - UK's hottest day ever. 8)


But - it doesn't have to be a heatwave to overheat and lose power. Hell - you can do that INDOORS on your turbo trainer.

Alex_Simmons/RST

Pokerface wrote:

July 19, 2006 - UK's hottest day ever. 8)

How hot was it?

Pokerface

Alex_Simmons/RST wrote:

Pokerface wrote:

July 19, 2006 - UK's hottest day ever. 8)

How hot was it?

20°C. This IS the UK after all.




(Edit - I think it was actually closer to 36° which is pretty pathetic compared to REAL hot weather).

Bhima

I'm going to Oman next winter, after seeing the wonderful lanscapes this week. I think i'll DIE though, being used to 10-20 in "summer".

amaferanga

Pokerface wrote:

But there are no hills in the UK that take an hour to get up! Longest one is all of about 20 minutes!

(But if not in the UK - I agree with you. It's easier to do higher wattages for longer times when on an incline.)

If you can get up the Bealach na Ba and Dufton Fell in 20 minutes then I suggest you give team Sky a call

Pokerface

amaferanga wrote:

Pokerface wrote:

But there are no hills in the UK that take an hour to get up! Longest one is all of about 20 minutes!

(But if not in the UK - I agree with you. It's easier to do higher wattages for longer times when on an incline.)

If you can get up the Bealach na Ba and Dufton Fell in 20 minutes then I suggest you give team Sky a call

The longest continuous climb in the UK is only about 5 miles long. Thus about 20 minutes of riding.


However - I was being technical about it and I'm sure there are longer 'climbs'. Just with little breaks in them.

chrisw12

Pokerface wrote:

Alex_Simmons/RST wrote:

Pokerface wrote:

July 19, 2006 - UK's hottest day ever. 8)

How hot was it?

20°C. This IS the UK after all.




(Edit - I think it was actually closer to 36° which is pretty pathetic compared to REAL hot weather).

and would have very little impact on climbing power.

Pokerface

chrisw12 wrote:

Pokerface wrote:

Alex_Simmons/RST wrote:

Pokerface wrote:

July 19, 2006 - UK's hottest day ever. 8)

How hot was it?

20°C. This IS the UK after all.




(Edit - I think it was actually closer to 36° which is pretty pathetic compared to REAL hot weather).

and would have very little impact on climbing power.

Sorry - but you are wrong, wrong, wrong on that account! Don't confuse the obvious energy-sapping 40°+ temperatures of a Vuelta climb with the loss of power you can get from overheating at ANY temperature.

If you have enough lack of ventilation, your body temperature will rise to the point where you lose power - no matter what the EXTERNAL temperature is. But you're still overheating.

Maybe you're confusing air temperature with body temperature?

It's easier to overheat at 40° - but you can still overheat at 0°.

chrisw12

Pokerface wrote:

chrisw12 wrote:

Pokerface wrote:

Alex_Simmons/RST wrote:

Pokerface wrote:

July 19, 2006 - UK's hottest day ever. 8)

How hot was it?

20°C. This IS the UK after all.




(Edit - I think it was actually closer to 36° which is pretty pathetic compared to REAL hot weather).

and would have very little impact on climbing power.

Sorry - but you are wrong, wrong, wrong on that account! Don't confuse the obvious energy-sapping 40°+ temperatures of a Vuelta climb with the loss of power you can get from overheating at ANY temperature.

If you have enough lack of ventilation, your body temperature will rise to the point where you lose power - no matter what the EXTERNAL temperature is. But you're still overheating.

Maybe you're confusing air temperature with body temperature?

It's easier to overheat at 40° - but you can still overheat at 0°.

I'm not confusing anything. OUTSIDE in this country you'd have to be a complete idiot to overheat. For staraters there is NOT a lack of ventilation. For seconders the human body has built some pretty good mechansisms for getting rid of heat.

I'd like to see what the person is wearing that manages to overheat at 0 c OUTSIDE in this country

See what master Bhima has now caused! We're miles away from the op!

Pokerface

chrisw12 wrote:

Pokerface wrote:

chrisw12 wrote:

Pokerface wrote:

Alex_Simmons/RST wrote:

Pokerface wrote:

July 19, 2006 - UK's hottest day ever. 8)

How hot was it?

20°C. This IS the UK after all.




(Edit - I think it was actually closer to 36° which is pretty pathetic compared to REAL hot weather).

and would have very little impact on climbing power.

Sorry - but you are wrong, wrong, wrong on that account! Don't confuse the obvious energy-sapping 40°+ temperatures of a Vuelta climb with the loss of power you can get from overheating at ANY temperature.

If you have enough lack of ventilation, your body temperature will rise to the point where you lose power - no matter what the EXTERNAL temperature is. But you're still overheating.

Maybe you're confusing air temperature with body temperature?

It's easier to overheat at 40° - but you can still overheat at 0°.

I'm not confusing anything. OUTSIDE in this country you'd have to be a complete idiot to overheat. For staraters there is NOT a lack of ventilation. For seconders the human body has built some pretty good mechansisms for getting rid of heat.

I'd like to see what the person is wearing that manages to overheat at 0 c OUTSIDE in this country

See what master Bhima has now caused! We're miles away from the op!

Oh jeez....

OK - riding in REALLY cold weather - you tend to wear a lot of thermal clothing. It's mostly designed to keep heat IN- and the cold OUT. That.... is a lack of ventilation.

Yes- you can simply take off a layer and cool down, etc. But if you happen to be doing a long climb, it is POSSIBLE to raise your body temperature under those conditions to the point where you lose power.

Over the winter my flat was easily 0° with the heat off. Once or twice I hopped on the turbo and didn't turn the fan on (thinking it was so cold I didn't need it). Didn't take long before I was overheated. And that was just in shorts.

It doesn't take much to lose power. We're not talking about "passed out on the side of the road from heat exhaustion" loss of power. Just enough overheating to lose SOME power.

ut_och_cykla

Well I for one have certainly felt overheated at about 1 or 2 C - well overdressed on a bike ride that went a lot harder and faster than I reckoned with ..which probably makes me a complete idiot in some peoples eyes but shows it is possible....
and it made me feel proper poorly after a while - If I opened up the jacket and various layers I froze, if I didnt I boiled! And I have 'enjoyed' airless rides in 35 C Provence where sweat never really gets a chance ... like walking into a sauna - walls of shimmering heat - but given the dryness it was actually preferable to the boil in a bag experience.

Alex_Simmons/RST

We just had our hottest February night in 70 years. It was 29C at midnight and a minimum of 26C.

sheffsimon

Alex_Simmons/RST wrote:

We just had our hottest February night in 70 years. It was 29C at midnight and a minimum of 26C.

Yeah, know how that feels, it was about that in Sheffield last night. :!:

Stephencp

Jibbering Jim - could you expand on your earlier comment about the the different inertial loading between hill climbing and riding on the flat and perhaps explain what effect this has on the rider.[/quote]